Method and device for optical form measurement and/or estimation

ABSTRACT

A method for optical shape recording and/or evaluation of optically smooth, glossy or optically rough surfaces wherein a photometric stereo method and a deflectometric method are combined using a scattering body so that the positions on the scattering body surface are two-dimensionally encoded.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a 35 U.S.C. §§ 371 national phase conversionof PCT/EP2003/013152, filed 22 Nov. 2003, which claims priority ofGerman Application No. 102 58 130.4, filed 29 Nov. 2002 and GermanApplication No. 103 45 349.0, filed 19 Sep. 2003. The PCT InternationalApplication was published in the German language.

BACKGROUND OF THE INVENTION

The invention relates to a method and a device for optical shaperecording and/or evaluation of objects and surfaces, in particularglossy surfaces. The term glossy refers below to objects whose opticalroughness lies in the transition range between optically rough andoptically smooth surfaces. Optically rough surfaces are defined ashaving a roughness which is substantially greater than the wavelength ofvisible light (about 0.5 micrometers), while optically smooth surfaceshave a roughness much less than the wavelength. Because of thisproperty, optically rough surfaces exhibit nondirectional, diffusereflection or transmission of light. Examples of this are paper, chalk,matt disks etc. Optically smooth surfaces, however, reflect or transmitincident light directionally. They are capable of producing an opticalimage of their surroundings. Examples which may be mentioned are flat orcurved mirrors and polished metal and glass surfaces (lenses).

In the transition range between these two extremes lie the objectsreferred to as glossy. These objects are of great importance since theyare encountered very often. In particular, industrially produced objectsof metal, plastic or even wood and other materials belong to glossyobjects. The industrial processing of such materials (machining of metaland wood, injection molding of plastic, powder injection of metal andceramic etc.) produces roughnesses in the range of a few micrometers,i.e. of the order of the wavelength of visible light (around 0.5micrometers).

There is a wide selection of optical 3D sensors for diffuselyscattering, optically rough surfaces. One of the most widespread methodsis based on the projection of strip patterns. The patterns are projectedin one direction and observed with a camera in another direction.Depending on the shape of the object being observed, the strips appearmore or less deformed to the camera. The shape of the object can beinferred from the deformation of the strips. More than three strippatterns are generally projected, with the intensity of the stripsassuming a sinusoidal profile.

Among the many other methods, the methods of the “shape from shading”group should be mentioned, in particular the photometric stereo methodsince the invention is based on it. From the brightness structure of anobject surface, these methods infer its shape. A detailed descriptionwill be given below.

Methods which allow three-dimensional measurement for smooth surfacesare also known. Primarily interferometric methods are employed fortesting simple surface shapes, such as flat or spherical surfaces(lenses, mirrors etc.). The Hartmann method or the Shack-Hartmann testare employed for more complexly shaped surfaces such as aspheres. Here,the deflection of a thin beam of rays by the object to be measured isobserved. Other methods observe a grid pattern which is reflected ortransmitted by the object surface. Depending on the shape of the latter,the grid appears more or less deformed. These methods can be combinedunder the heading deflectometric methods. A feature common to them isthat the ray deflection is determined and the shape of the surface isinferred therefrom. The deflectometric methods are based on thereflection law or refraction law, which describes the relation betweenan incident ray, surface normal and the reflected or transmitted ray.

The measurement of surfaces in the transition range between opticallyrough and optically smooth surfaces, however, has not yet been resolved.The methods of both categories are deficient in this case. Although asensor for rough surfaces can cope with occasionally occurring glossypoints, such a sensor is unsuitable when gloss dominates over diffusescattering. On the other hand, a sensor for optically smooth surfaces,in particular a deflectometric sensor, will have difficulty when thesurface is too rough to allow clear optical imaging. For example, it isnecessary to ensure that the fine structure of the grid is stillvisible. The method with sine strips places less stringent requirementson the quality of the surface, since sinusoidal strips allow a greaterdegree of haziness. But even here it is necessary to ensure that thestructure of the strips is still visible.

The known optical sensors thus do not provide satisfactory resultsprecisely for glossy surfaces in the transition range, which occur veryfrequently in industrially manufactured products.

It is therefore an object of the invention to provide a method and adevice which avoid this disadvantage.

SUMMARY OF THE INVENTION

This object is achieved by a method having the features of theinvention. It is distinguished in that two methods known per se, whichseem mutually incompatible at first sight, are combined with the aid ofa specially shaped optical element, in particular a scattering body. Oneof them is a photometric stereo method known per se. This method isemployed for diffusely reflecting surfaces, but is deficient for glossysurfaces. The other is a deflectometric method for reflecting ortransmitting surfaces. The application ranges of the two methods areexpanded by the optical element, so that the resulting overall methodprovides particularly good results for glossy surfaces.

This object is also achieved by a device having the features of theinvention. It is distinguished by a scattering body. This makes itpossible to expand the application ranges of different methods ofoptical shape recording so that methods hitherto mutually exclusive onone body, in particular the deflectometric method and photometric stereocan advantageously be combined to form a new method, preferably forbodies with glossy surfaces.

An exemplary embodiment of the device which is distinguished in that thescattering body at least partially has a spherical, ellipsoid and/orrotationally symmetric structure is preferred. This offers the advantagethat when the scattering body is illuminated, the radiation coming fromit can be utilized very easily with the aid of known mathematicalrelations for recording the shape of an object.

Lastly, an exemplary embodiment in which a microscope and/or microscopeobjective is used for the optical imaging is preferred. This makes itpossible to record the shapes of particularly small objects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to apresentation of the combined method according to the invention and adrawing, in which:

FIG. 1 shows a known method for carrying out a photometric stereomethod;

FIG. 2 shows a partial representation of a known device for carrying outa deflectometric method; and

FIG. 3 shows a schematic representation of an exemplary embodiment of adevice for carrying out the optical shape recording method according tothe invention.

DESCRIPTION OF PRIOR ART AND A PREFERRED EMBODIMENT OF THE INVENTION

The photometric stereo method belongs to a larger group of methods,which are known by the name “shape from shading”. This methods involvesusing the variation of the brightness in an image to infer the shape ofthe object being imaged. If the photograph of a face is observed, forexample, then brightness fluctuations are found even though it can beassumed that the reflection coefficient of the skin scarcely changes.Rather, these fluctuations are due to particular parts of the surfacebeing oriented so that they radiate more light to the camera than othersdo. The brightness is maximal when the light from a source strikes thesurface perpendicularly, while it is minimal with grazing incidence. Aclear example is also provided by the illumination of the Earth'ssurface by the sun. The sun shines almost perpendicularly onto theEarth's surface at midday in summer, which leads to a high level ofbrightness. At sundown, the light just grazes the surface and there islow level of brightness. There are various formulations of shape fromshading.

One group of methods deals with determining the shape of a surfaceassumed to be untextured (the same reflection coefficient everywhere).Other methods determine the position of the light source in addition tothe shape of the object (source from shading). As regards thephotometric stereo method, the position of the light source is known apriori and object texture is allowed. This is particularly importantwith a view to a versatile sensor since the texture is usually unknownin practice. A photometric stereo method will therefore be involvedbelow.

The photometric stereo method which can be carried out with a deviceaccording to FIG. 1 will be presented here. It is assumed that an objectG to be measured, which has the three-dimensional shape z(x,y), isilluminated successively from three point light sources 1, 2, 3. In FIG.1, the surface O of the object G is indicated by a line. In the simplestcase, it can be assumed that the light sources are a large distance awayand the illumination direction therefore remains constant over theobject G for every source. The situation is particularly straightforwardwhen the surface O can be represented as a Lambert scatterer (idealnondirectional scattering). For a Lambert scatterer, the intensityscattered by the object G depends only on the illumination direction andthe gradient of the object G, but not on the observation direction. Acamera K takes a separate image for each of the three light sources 1,2, 3. The positions of the object G and camera K remain fixed duringthis.

Mathematical representation of the photometric stereo method requiresthe three illumination directions and the normal vector n(x,y) of thesurface O of the object G, also referred to as the object surface. Theillumination directions are described by the vectors s ₁, s ₂ and s ₃.They point from the object surface to the light source in question.s ₁=(s ₁₁ , s ₁₂ , s ₁₃)^(T)s ₂=(s ₁₂ , s ₂₂ , s ₂₃ )^(T)s ₃=(s ₃₁ , s ₃₂ , s ₃₃ )^(T)

Since the light sources are a large distance away, these vectors remainapproximately constant for all points of the surface O. The normal(perpendicular to the surface) vector n(x,y), however, varies accordingto the shape of the surface O and should be interpreted as a localnormal vector.n (x,y)=(n _(x)(x,y), n _(y)(x,y), n _(z)(x,y))^(T)

It will be assumed that the surface z(x,y) is differentiable and thenormal vector exists everywhere. In the event that z(x,y) is notdifferentiable owing to edges or discontinuities, the surface may bedivided into differentiable sections. The camera K takes the imagesE₁(x,y) , E₂(x,y) and E₃(x,y) of the object G, i.e. one image per lightsource 1, 2 and 3. The camera K is a large distance away in thedirection of the z axis, and each pixel receives the incidentillumination strength E₁(x,y) with i=1, 2, 3, which can be allocated tothe coordinates (x,y) of the surface O. According to Lambert's law, thescattered luminance varies with the cosine between the illuminationdirection s _(i) and the normal vector n(x,y). As an alternative, thescattered luminance may also be expressed via the scalar product of theillumination direction and the normal direction. The advantage of thisrepresentation is that the relationships can be represented linearly.Besides the gradient of the surface O and the illumination direction,the scattered luminance also depends on the local reflection coefficientρ(x,y) of the surface O (texture) and the illumination strength of thelight sources and the parameters of the camera optics. All the constantfactors, such as the illumination strength of the light sources and theparameters of the camera optics, are combined in the length of theillumination vector. It is therefore possible to writeE ₁ =ρ· s ₁ · nE ₂ =ρ· s ₂ · nE ₃ =ρ· s ₃ · n

These three equations can be combined to form a single equation inmatrix notation, if the following notation is introduced for the images.Ē=(E ₁ ,E ₂ ,E ₃)^(T)

The illumination vectors form the rows of the illumination matrix

$S = \begin{pmatrix}S_{11} & S_{12} & S_{13} \\S_{21} & S_{22} & S_{23} \\S_{31} & S_{32} & S_{33}\end{pmatrix}$

It is therefore possible to writeĒ=ρ·S· n

Solving for n or ρ gives

$\overset{\_}{n} = {{{\frac{1}{\rho} \cdot S^{- 1} \cdot \overset{\_}{E}}\mspace{14mu}\text{with}\mspace{14mu}\rho} = {{S^{- 1} \cdot \overset{\_}{E}}}}$

The illumination matrix S can always be inverted if the illuminationvectors are linearly independent, i.e. when the object G and the threelight sources 1, 2, 3 do not lie in a plane.

This mathematical description of the photometric stereo method with theaid of vectors offers the advantage over other descriptions (forexample, descriptions with the aid of angles) that a linear relation isobtained between the normal direction, the illumination directions andthe illumination strengths E₁, E₂ and E₃. This linear relation canreadily be solved mathematically for the quantity of interest, thenormal direction: it is merely necessary to invert the illuminationmatrix. Three-dimensional illumination arrangements in which the normaldirection and the various illumination directions do not lie in a planecan therefore be handled well, which is not possible for otherdescriptions (for example, descriptions with the aid of angles). This isof great importance in what follows for the method according to theinvention, since it is also based on a vector description and cantherefore accommodate three-dimensional illumination arrangements andmeasure three-dimensional objects. Once the normal vector has beendetermined, the shape of the object surface z(x,y) can easily berepresented with the aid of the partial derivatives p and q with respectto x and y. This is advantageous for the subsequent integration of theshape z (x,y).

$p = {\frac{\partial z}{\partial x} = {- \frac{n_{x}}{n_{z}}}}$$q = {\frac{\partial z}{\partial y} = {- \frac{n_{y}}{n_{z}}}}$

This description of photometric stereo is valid for Lambert surfaces andlight sources far away. This special case was selected in order to beable to present the function of the method as simply as possible. It ispossible to adapt the method for light sources a finite distance awayand surfaces which do not obey the Lambert law, although this will notbe pursued here.

So far, the shape data of the surface O are provided as a normal vectorn(x,y) or as partial derivatives (also referred to here as the localgradient)

$p = {\frac{\partial z}{\partial x} = {- \frac{n_{x}}{n_{z}}}}$$q = {\frac{\partial z}{\partial y} = {- {\frac{n_{y}}{n_{z}}.}}}$In order to obtain the shape z(x,y), it is necessary to integrate thepartial derivatives.

Besides the photometric stereo method, the invention also utilizesdeflectometry. A feature common to deflectometric methods is that theydetermine the deflection of a ray by a reflecting or transmittingsurface, and infer its shape therefrom. They are based on the reflectionlaw or refraction law, which describes the relation between an incidentray, the surface normal and the reflected ray (see FIG. 2). FIG. 2 showsa device having a camera K which is aimed at an object G illuminated bya light source L, in order to record its surface O. In the case ofreflection, the incident ray E, reflected ray R and surface normal m liein a plane. The angles between the incident ray and the surface normal,and between the reflected ray and the surface normal, are equal. Asimple description can be obtained if the incident ray E is denoted bythe unit vector from the surface O in the direction of the light sourceL, and the reflected ray R is similarly denoted by the unit vector fromthe surface O in the direction of observation b. The normal vector thenforms the sum (normalized to a length of one) of the vectors of theincident ray E and of the reflected ray R.

Deflectometric methods have previously been used for optically smoothsurfaces. The photometric stereo method and the deflectometric methodseem mutually incompatible at first sight, since the surface to bemeasured cannot simultaneously be optically rough and optically smooth.Nevertheless, the two methods can be advantageously combined if asuitable optical element is introduced. The combination of the twomethods will be referred to below as “photometric deflectometry”. Thisoptical element is a suitably shaped, preferably hemisphericaltranslucent scattering body, in particular at least partially with anrotationally symmetric structure. The deflectometric part of the methodfinds its counterpart in the glossy surface of the specimen, and thephotometric in the scattering body. With the described combination ofthe method, it is possible to measure very glossy surfaces.

A device for photometric deflectometry is represented in FIG. 3, and ispreferably constructed as follows: a camera K is aimed at a glossyobject G, also referred to as the specimen. Its surface O reflects lightcoming from a preferably hemispherical scattering body S in thedirection of the camera K. If the method is to be used in transmissioninstead of reflection, the camera K must be aimed at the object G in theopposite direction, here from below. Owing to its roughness, the objectG generates a more or less blurred image of the scattering body S ratherthan a clear one. The blurred image does not represent an hindrance forthe method, and as would otherwise be the case with deflectometricmethods. This will be dealt with in more detail below. For its part, thescattering body S is illuminated by a plurality of light sources 1, 2,3, . . . (preferably three), as is usual for photometric methods. Theassociated illumination vectors from a point P of the scattering body S,selected by way of example, to the light sources are s ₁, s ₂ and s ₃.The object G and the light sources 1, 2, 3 preferably do not lie in thesame plane but are arranged spatially, in three dimensions.

Preferably, the light source 1 is switched on initially, the othersbeing switched off, and the camera K takes an image 4 a of the object Gunder these illumination conditions. This procedure is repeated afterthe light source 2 has been turned on and the other light sources havebeen switched off, and likewise for light source 3 etc. Images 4 b, 4 cetc. are thereby taken. Optionally, the light sources may be switched onin a different sequence. Likewise, the light sources may be switched ontogether, for example light sources 1 and 2, then light sources 2 and 3,and lastly light sources 3 and 1. Arrangements with more or fewer thanthree light sources are also possible.

The recording is followed by evaluation of the images 4 a, 4 b, 4 caccording to the photometric stereo method. As described above, thenormal vector n(x,y) or the gradient of the scattering body S can beinferred from the position of the light sources 1, 2, 3 and the grayvalues of the image points of the images 4 a, 4 b, 4 c.

$\overset{\rightharpoonup}{n} = {\frac{1}{\rho} \cdot S^{- 1} \cdot \overset{\rightharpoonup}{E}}$with $\rho = {{S^{- 1} \cdot \overset{\rightharpoonup}{E}}}$

This is the surface normal of the object G in the conventionalphotometric stereo method, but it is the normal of the scattering body Sin photometric deflectometry. This is a very essential innovation: Thephotometric stereo method is used to uniquely encode every position onthe scattering body surface. The encoding may be thought of as dividedinto various steps:

-   -   The shape of the scattering body is selected so that every        position on the scattering body surface has a normal vector n        which occurs only once. It is preferably a sphere, an ellipsoid,        a rotationally symmetric body or parts thereof. Reciprocally,        for each normal vector there is only one position on the        scattering body. The allocation is therefore unique.    -   Furthermore, the photometric stereo method allocates the        back-scattered luminances to each normal vector n of the        scattering body surface and vice versa.    -   The luminances back-scattered by the scattering body are in turn        allocated uniquely to the illumination strengths E₁, E₂ and E₃        of the camera images via the reflection at the object surface.

If the position on the scattering body is now uniquely allocated to thenormal vector n, the latter is uniquely allocated to the back-scatteredluminance and this is in turn allocated to the illumination strengthsE₁, E₂ and E₃ of the images recorded by the camera, then the positionand illumination strengths are uniquely allocated to one another. Fromthe illumination strengths in the images, it is therefore possible todeduce which position of the scattering body has scattered the light.This means that the scattering body surface has been uniquely encoded.With just three illumination directions, any position of the scatteringbody surface can be encoded unequivocally in three-dimensional space.This encoding has clear advantages over other methods which, forexample, locally illuminate the scattering body step by step. Suchmethods require a multiplicity of illumination directions but can onlyrecord a single line on the scattering body, which corresponds totwo-dimensional recording of the object.

With the method according to the invention, conversely, with just threeillumination directions it is possible to two-dimensionally encode thescattering body and therefore allow three-dimensional measurement of theobject. The normal m(x,y) of the object surface is then determined fromthe unique encoding of the position and from the normal vector on thescattering body.m (x,y)=(m _(x)(x,y),m _(y)(x,y),m _(z)(x,y))^(T)

A scattering body S designed as a sphere will be considered below. Inparticular, a spherical surface has the special property that every unitvector r(x,y) from the center in the direction of the surface (radialvector) is parallel to the normal vector n(x,y) at this point (see FIG.3). The radial vector and the normal vector of the object G are in turnrelated to one another via the reflection law or refraction law(deflectometry). If the object G is small compared to the radius of thesphere, then all object points lie approximately at the center of thesphere. The normal vector on the object can be calculated even withoutthis assumption, but a small object will be assumed here in order toallow a simple presentation. The z axis of the coordinator system isselected so that it extends parallel to the optical axis of the cameraK. According to the reflection law, the following applies for the normalvector m(x,y) of the surface m(x,y)=const·( n+ b) with the unit vectorin the direction of observation b and the constraint that m and n areunit vectors. It is therefore possible to determine the normal vector ofthe object G for a multiplicity of points of the object surface O, thepartial derivatives p and q from this, and from these in turn the shapeof the surface z(x,y) of the object G by integration.

Yet even without integrating the local gradients p(x,y) and q(x,y) toform z(x,y), it is already possible to draw valuable conclusions aboutthe object surface. Contrary to expectation, it is even expedient tostop at the evaluation actually before the integration step. Agraphical, grayscale representation of the gradient (intermediateresult) is in fact preferable to a graphical representation of z(x,y)(final result) for many applications. This is surprising insofar as afinal result generally contains more information than an intermediateresult. The same applies for a representation of the local normal vectorof the object surface, or its components. The gradient and normal vectorare directly related so that, for the following argument, the term“gradient” may also be replaced by the term “normal vector” or itsrespective components.

The gradient representation offers advantages, in particular, when thetask is to represent the shape of the surface to a human observer(visualization) or to analyze distinctive features (interpretation,evaluation). The gradients p(x,y) and q(x,y) are output as grayscaleencoded images on a monitor, printer etc. The gradient representationbrings out even very small indentations, elevations, grooves and ridges.

The advantages of the gradient representation are based on the fact thatthe human visual faculty is by its very nature accustomed tointerpreting gradient data. Human vision uses brightness shadings (as inshape from shading and the photometric stereo method) to obtain aspatial conceptualization of the object being observed. There arefurthermore other mechanisms, for example stereo vision, which alsocontribute to spatial impression. Compared to the other mechanisms ofspatial vision, gradient vision is the most accurate source ofinformation. With suitable illumination and a suitable viewing angle,experienced observers are capable recognizing irregularities of lessthan 10 micrometers from the shading itself. Besides shadings, lightreflections from an object or specimen (as in the deflectometric method)impart a spatial impression which allows extremely fine details to berecognized.

If the grayscale encoded gradient representation is combined with agradient measuring method, such as the photometric stereo method orphotometric deflectometry, even irregularities that cannot be seen bythe human eye on the real object can be made visible. For humans,texture (local brightness) and gradient information of the object arealways mixed. For example, it is difficult to assess whether a lineperceived as dark on an object is due to a shape feature, for example agroove, or a darkly colored marking. Photometric deflectometry and thephotometric stereo method can offer assistance here. They take more thanone illumination situation into account (unlike the visual faculty) andmake it possible to separate gradient data from texture. When visualizedas a gradient image, even invisible features can thus be made visible.

The combination of gradient measurement and gradient representation alsooffers advantages in terms of accuracy. It is possible to record detailsin the range of a few micrometers. The gradient is visualized and theshading effects can be computationally emphasized and accentuated.

These gradient measuring methods are furthermore robust with respect totilting and rotation of the object relative to the illumination. Forexample, the human observer can recognize a flat indentation on a glossyobject only with a very particular direction of the illumination. Thesituation is similar with many image processing methods. The choice ofillumination is particularly critical for glossy surfaces. If only verysmall changes in the position of the object surface occur with respectto the illumination, for example due to inaccuracies in the delivery ordeviations of the object itself, then the view of the surface changesfundamentally because of differing light reflections. The case is verydifferent with the photometric deflectometric method. Reproduciblemeasurements and objective evaluation are possible even for a tiltedglossy object. The gradient representation is furthermore advantageousfor the automatic machine evaluation of surfaces. The data processed asa gradient facilitate automatic evaluation, or make it possible for thefirst time, preferably by a computer or another electronic analysisunit. The aforementioned advantages of gradient representation applyaccordingly for automatic evaluation.

Owing to the many advantages of a gradient representation, it could alsobe envisaged for other methods which record the shape z(x,y) directly.The gradients p(x,y) and q(x,y) could then be obtained by numericaldifferentiation. It should, however, be borne in mind thatdifferentiation amplifies particularly the high-frequency noise which iscontained in any real measurement. This is not the case with thegradient measuring methods, in particular photometric deflectometry andthe photometric stereo method. In this case, the gradient is measureddirectly. Although minor measurement noise is also contained here, thestep of numerical differentiation which could worsen this noise isobviated.

A gradient measuring method together with a gradient representation isthus an advantageous combination of a measuring method andvisualization.

At this point, it should also be mentioned that the photometricdeflectometry method can even be used for optically rough surfaces. Theobject surface delivers a more or less blurred image of the scatteringbody S. In other deflectometric methods, this is a problem since finelystructured patterns such as strips, points etc. generally need to beimaged. This is not the case with photometric deflectometry. Thebrightness on a spherical scattering body varies so uniformly thatdistortions can scarcely occur even with very blurred imaging.

Photometric deflectometry is therefore superior to other deflectometricmethods for rough and smooth glossy surfaces. Moreover, it is alsosuperior to the photometric stereo method which can only be used fordiffusely scattering surfaces.

Another advantage of this method is that just three camera recordings(corresponding to three illumination directions) are sufficient fordetermining the shape of the object. The time for a complete measurementcan therefore be kept very short, as is desirable in industrialmeasuring and testing technology. A further reduction to merely a singlecamera recording is achieved, in particular, when the three lightsources are encoded in the colors red, green and blue and an electroniccolor camera K is used for the observation. The color channels red,green and blue contain the images 4 a, 4 b, 4 c of the correspondinglyencoded illumination directions. There is, however, a precondition thatthe object must be one-colored. Reducing a measurement to a singlecamera recording represents a crucial advance. With a correspondinglyshort exposure time, similarly as flash lamp recording in photography,even moving objects can be recorded without sufficient motion blurring.

The discussion so far has assumed that glossy objects are intended to bemeasured. The described method and the associated device maynevertheless also be used beneficially for diffusely scattering objects.On these surfaces, the principle of photometric stereo does not retaindirectly to the scattering body 1, but instead the object itself. Thescattering body 1 together with the light sources 1, 2, 3 etc. act likea series of extended light sources. Spatially extended light sourceshave the advantage that they can minimize coherent optical noise due tospeckling. Coherent noise has repercussions on the shape measurementinaccuracy in all optical 3D sensors. The described method thereforemakes it possible to reduce the measurement inaccuracy for diffuseobjects. This property is furthermore conducive to a precise measurementof glossy surfaces.

It is particularly preferable for the results of the shape measurementto be provided as a software file. This facilitates their furtherprocessing.

It is furthermore possible to use a microscope and/or a microscopeobjective for the optical imaging. In this way, the existing optics ofthe camera K are replaced and/or supplemented so that even the surfacesof particularly small objects can be measured.

Light-emitting diodes (LEDs) may preferably be used for theillumination. These are convenient to produce and can be operatedrapidly and straightforwardly.

Lastly, it is conceivable to use one or more flash lamps for theillumination. Owing to the short illumination time of flash lamps, thiscan reliably avoid any measurement errors due for example to relativemotion between the light source, camera K and the object to be measured,which may for example be attributable to vibrations or moving objects.Furthermore, flash lamps advantageously have a high luminosity so thatthe camera K may accordingly be designed with a lower photosensitivity.

1. A method for at least one of optical shape recording and evaluationof an optically smooth surface, an optically glossy surface or anoptically rough surface, the method combining a photometric stereomethod and a deflectometric method, the method comprising:two-dimensionally encoding positions on a surface of a scattering bodywith reference to a shape of the scattering body, such that one vectornormal to each position on the surface of the scattering body isuniquely allocated to each position on the scattering body surface;uniquely allocating to each normal vector a luminance back-scattered bythe scattering body; and allocating the back-scattered luminance toillumination strengths of recorded images.
 2. The method as in claim 1,wherein the scattering body has a shape of a sphere, an ellipsoid, arotationally symmetric body or parts thereof.
 3. The method as in claim1, further comprising providing a result of the at least one of opticalshape recording and the evaluation in a form of a software file.
 4. Themethod as in claim 1, wherein the at least one of optical shaperecording and evaluation is performed via an electronically operatingcamera.
 5. The method as in claim 4, wherein the camera is a colorcamera.
 6. The method as in claim 1, further comprising illuminating thesurface with color-coded illumination.
 7. The method as in claim 1,wherein the scattering body comprises an extended luminous scatteringbody surface for reducing coherent speckle noise.
 8. The method as inclaim 1, wherein the at least one of optical shape recording andevaluation comprises at least one of visualizing and electronicallyevaluating at least one of a local gradient and a local normal vector ofthe surface.
 9. The method as in claim 7, comprising at least one ofvisualizing and electronically evaluating at least one component of atleast one of a local gradient and a local normal vector of the surface.10. The method as in claim 8, wherein the at least one of the localgradient and the local normal vector is represented by being encoded asat least one of a grayscale and a color shade.
 11. The method as inclaim 9, wherein the at least one component of the at least one of thelocal gradient and the local normal vector of the surface is representedby being encoded as at least one of a grayscale and a color shade.
 12. Adevice for optical shape measurement for at least one of optical shaperecording and evaluation of an optically smooth surface, an opticallyglossy surface or an optically rough surface by combining a photometricstereo method and a deflectometric method, the device comprising: ascattering body comprising a scattering body surface; at least oneoptical recorder for receiving illumination reflected off the surface;at least one light source positioned to scatter illumination to thescattering body surface; a processor-readable medium incorporatingtwo-dimensionally encoded positions on the scattering body surface withreference to a shape of the scattering body, such that one vector normalto each position on the scattering body surface is uniquely allocated toeach position on the scattering body surface; and a processor operableto uniquely allocate to each normal vector a luminance back-scattered bythe scattering body and to allocate the back-scattered luminance toillumination strengths of recorded images.
 13. The device as claimed inclaim 12, wherein the scattering body has at least one of at leastpartially a spherical, ellipsoid and rotationally symmetric structure.14. The device as in claim 12, further comprising using at least one ofa microscope and a microscope objective for the optical imaging.
 15. Thedevice as in claim 12, wherein the light source comprises at least onelight-emitting diode for the illumination.
 16. The device as in claim12, wherein the light source comprises at least one flash lamp for theillumination.
 17. The device as claimed in claim 12, wherein the opticalrecorder comprises a camera.
 18. The method as claimed in claim 1,comprising three light sources positioned and configured forilluminating the surface.